The Entomologist’s Garden: Bumblebees

By Regina Johnson, CR

Who doesn’t like bumblebees? They’re so cute and furry and friendly. They bumble about the garden, deceptively clumsy, bold shiny black coats with yellow or white or orange markings, visiting flowers and knocking them over with their weight and getting covered with pollen. They don’t sting — usually. I’ve only known one person to get stung by a bumblebee and that was a 2-year old who picked one up and squeezed it. You’d sting too.

Honeybees are not native to North America and they don’t like Olympia’s cool damp climate. They’re Mediterranean insects who like it warm and dry. Bumblebees are different. They are native here. There are 18 different species of bumbles in Washington alone and about 50 in North America. They thrive in our cool damp climate. Sure, some live in deserts and semi tropical areas, but others range as far north as the Arctic Circle. They can operate at much lower temperatures than honeybees can, so they are often the first bees you see in spring — usually March but sometimes on warm days in February.

The first bumbles you see in spring seem huge and they are. With bumblebees it’s only the queens that overwinter, not workers. The first bees out in spring are the queens, building their nest and foraging to feed the first batch of young. Only once those young have matured into worker bees will the queen retire to the nest. After that, all the bumbles you see are the smaller worker bees. The first generation of workers are very small as the queen had to feed them all by herself. Later generations get progressively larger as more workers are available to feed the next generation. Towards the end of summer, the queen produces males and new queens for next year’s nests. You’ve probably seen male bumblebees without knowing it. They live outside the nest, so when you find bumbles sleeping on flowers early in the morning at the end of summer, those are the males.

The yearly life cycle of the bumblebee colony from Bumblebees by Prys-Jones and Corbet.

Bumblebee nests are usually underground in an old vole nest, but they can also be in a clump of grass, a woodpile, a broken pot laying on the ground or an old bird nest, depending on the species of bee. They don’t live in hives like honeybees do, and their colonies are usually much smaller since each one starts from a single queen every spring. Workers and males only live a few weeks while queens live about a year. Bumblebees make honey but not much. Like honeybees, bumbles eat pollen and nectar, and they visit many of the same kinds of flowers. That means bumbles like roses! Bumbles are important pollinators for flowers, vegetables, orchards, berries and wildflowers. They start work earlier in spring than honeybees do, as well as starting earlier in the day and work on colder and wetter days than the honeybees can. Bumblebees can actually “shiver” to raise their internal temperature and get their wing muscles warm enough to fly on cold days when honeybees are confined to their hives. Bumbles also can pollinate flowers that honeybees can’t. They have longer tongues for reaching into things like penstemons, and they do something called “buzz pollinating” on tomatoes, peppers and cranberries where they climb inside the flower and shake the pollen off by vibrating their wing muscles. Lack of pollination is a big problem for tomato, pepper and cranberry growers around here. They require buzz pollination, which only the bumblebees can do; so if you’re trying to grow tomatoes or the tree
fruits or blueberries blooming in cooler weather, you need bumbles.

Some bumblebee populations are declining, especially those of Bombus occidentalis here in western Washington. This bumble used to be common and widespread but is now thought to be extirpated in western Washington, Oregon and British Columbia. Culprits are thought to include insecticide use, diseases introduced by commercial beekeeping and habitat destruction. In the 1990s, B. occidentalis bees were collected for commercial propagation as pollinators for greenhouse tomatoes and sent to France for propagation. After French-propagated bees were brought back to the western US and released in greenhouses to work, the wild populations started declining rapidly, leading to speculation that the French-propagated bees brought a European bee disease with them. Sound far-fetched? It isn’t, unfortunately pretty much the exact same thing happened to western white pines, Pinus monticola.

Many insecticides are poisonous to bees. It’s important to follow label directions when applying insecticides, as the directions will include methods of reducing direct hazards to bees. But keep in mind that the studies done for pesticide registrations look at direct harm to honeybees only and are pretty minimal. I read pesticide registration documents at work and I’m not impressed with the amount of research
that goes into environmental fate and hazards to non-target organisms — big conclusions being drawn from just a little tiny bit of data. Longer-term studies done by independent organizations like the Xerces Society and OSU find that insecticide hazards to bees of all kinds are much more widespread than registration studies show.

As gardeners there’s not much we can do about introduced bee diseases, but we are responsible for habitat destruction. Bumblebees need uncultivated, undisturbed, insecticide-free ground for nesting and overwintering in. The queens dig into soft, well-drained soil on a slight slope to spend the winter. Fence-to-fence intensive gardening doesn’t leave the bumbles any place to build their nests or overwintering
burrows.

Soil insecticides don’t help either, since bumbles nest underground. If you’re using insecticides on the lawn for crane fly, or in the garden for carrot maggots or rose midge or strawberry root weevils. Sevin, Merit (imidacloprid), diazinon, permethrin, spinosad, and Orthene are all very toxic to bees — even when used as directed. If you’re using these, don’t apply them when bees are present or broadcast them throughout the garden or treat soil where bumbles might be nesting. Avoid spraying flowers, and spray late in the evening if you have to spray flowers. If you’re spraying for thrips, spray the flower buds just as the sepals crack — that’s when the thrips are getting in anyway, and it saves the bees from direct contact. Imidacloprid in particular shows up in the pollen and nectar the bees are eating since it’s systemic
and it’s very persistent in soil — up to three years! Petroleum oils, either as horticultural oils or as spreader-stickers, are also toxic to bees. Fortunately we don’t need much in the way of insecticides in Olympia.

Fungicides are generally considered safe for bees, but check out the literature I’ve posted on the website — copper sulfate and sulfur fungicides are toxic to bees. http://olyrose.org/articles.htm

To help the bumblebees in your garden you can plant early blooming flowers they can feed off of until the roses are blooming. Make sure you have single or semi-double or low-petal count roses in your collection —i f you can’t see the stamens, the bees can’t feed off it. In addition to roses, early blooms bumbles love include rhodies, pieris, crocus, tulips, balsamroot, grape hyacinth, camas, Indian plum, heather, violas, peas, lupines, mahonia, ceanothus, huckleberries and foxgloves, along with all the tree, bush and cane fruits. What a lovely garden these would make! And all dancing with the weight of bumblebees!

Bumblebees animate the garden and they like roses. They’re big and easy to see, and they come in different color patterns, all on a bold black background. They’re not aggressive. They appreciate the work we do to provide roses for them to feed from, and we aren’t using the pollen they’re eating anyway. And we like photos of roses with bees in them! All that on top of important pollination services to provide us with food like apples, tomatoes, cranberries, blueberries, raspberries, sunflower seeds, etcetera. How could you not like bumblebees?